U.S. patent number 5,833,442 [Application Number 08/751,018] was granted by the patent office on 1998-11-10 for scroll-type compressor having improved pressure equalizing passage configuration.
Invention is credited to Yong Hun Cho, Do Sig Choi, Wan Pyo Park, Hiun Won.
United States Patent |
5,833,442 |
Park , et al. |
November 10, 1998 |
Scroll-type compressor having improved pressure equalizing passage
configuration
Abstract
A scroll-type compressor has a scroll plate with at least first
and second pressure equalizing passages formed in its end plate
such that the first and second pressure equalizing passages will be
in the same crescent shaped pocket during at least a portion of a
crescent shaped pocket's radially inward movement. The minimum
pressure in a back pressure pocket will be adequate to maintain a
good seal, any pressure increases will increase in accordance with
the increased pressure in the crescent shaped pockets. At no point
are both of the pressure equalizing passages blocked and,
therefore, the pressure in the interior space does not overwhelm
the effective functioning of the back pressure pocket.
Inventors: |
Park; Wan Pyo (Asan City,
Chungnam, KR), Won; Hiun (Seoul, KR), Choi;
Do Sig (Asan City, KR), Cho; Yong Hun (Asan City,
KR) |
Family
ID: |
19434597 |
Appl.
No.: |
08/751,018 |
Filed: |
November 15, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Nov 18, 1995 [KR] |
|
|
1995-42098 |
|
Current U.S.
Class: |
418/1; 418/55.5;
418/57 |
Current CPC
Class: |
F04C
27/005 (20130101) |
Current International
Class: |
F04C
27/00 (20060101); F04C 018/04 () |
Field of
Search: |
;418/1,55.5,57 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
53-119412 |
|
Oct 1978 |
|
JP |
|
4-219485 |
|
Aug 1992 |
|
JP |
|
Primary Examiner: Vrablik; John J.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Claims
What is claimed is:
1. A scroll plate for use in a scroll-type fluid compressor,
comprising
an end plate having a center point, and a spiral shaped wrap for
interfitting with a spiral shaped wrap on a second scroll plate to
thereby form a series of moveable, crescent-shaped pockets which
reduce in volume as the plates rotate relative to each other about
the center point;
said end plate having a first pressure equalizing passage formed
through the plate at a distance from said center point and a second
pressure equalizing passage formed through the plate at a distance
from said center point, wherein
said first and second pressure equalizing passages are positioned
at locations in the end plate that permit said first and second
pressure equalizing passages to be in the same crescent shaped
pocket at some time, but prevent said first pressure equalizing
passage from being open in a crescent shaped pocket at the same
time said second pressure equalizing passage is open in a different
crescent shaped pocket when the plates rotate relative to each
other to thereby prevent pressure leakage between high and low
pressure crescent shaped pockets.
2. The scroll plate of claim 1, wherein
a line from said center point to said first pressure equalizing
passage and a line from said center point to said second pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
3. The scroll plate of claim 1, wherein
said spiral shaped wrap has a wall thickness, said first and second
pressure equalizing passages are holes having a diameter, said wall
thickness being greater than or substantially equal to said hole
diameter so that the spiral shaped wrap completely covers each hole
at some time when the plates rotate relative to each other.
4. The scroll plate of claim 3, wherein
said wall thickness is substantially equal to said hole
diameter.
5. The scroll plate of claim 1, wherein
said end plate has third and fourth pressure equalizing passages
formed through the plate, said third pressure equalizing passage
being formed at a distance from said center point and offset
180.degree. from said first pressure equalizing passage, said
fourth pressure equalizing passage being formed at a distance from
said center point, wherein
said third and fourth pressure equalizing passages are positioned
at locations in the end plate that permit said third and fourth
pressure equalizing passages to be in the same crescent shaped
pocket at some time when the plates rotate relative to each
other.
6. The scroll plate of claim 5, wherein
a line from said center point to said third pressure equalizing
passage and a line from said center point to said fourth pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
7. A scroll plate for use in a scroll-type fluid compressor,
comprising
an end plate having a center point, and a spiral shaped wrap for
interfitting with a spiral shaped wrap on a second scroll plate to
thereby form a series of moveable, crescent-shaped pockets which
reduce in volume as the plates rotate relative to each other about
the center point;
said end plate having a first pressure equalizing passage formed
through the plate at a distance from said center point and a second
pressure equalizing passage formed through the plate at a distance
from said center point, wherein
said first and second pressure equalizing passages are positioned
at locations in the end plate that prevent said first and second
pressure equalizing passages from simultaneously being completely
blocked by the spiral shaped wrap of the second plate and from
simultaneously being open in different crescent shaped pockets at
any time when the plates rotate relative to each other.
8. The scroll plate of claim 7, wherein
a line from said center point to said first pressure equalizing
passage and a line from said center point to said second pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
9. The scroll plate of claim 7, wherein
said spiral shaped wrap has a wall thickness, said first and second
pressure equalizing passages are holes having a diameter, said wall
thickness being greater than or substantially equal to said hole
diameter so that the spiral shaped wrap completely covers each hole
at some time when the plates rotate relative to each other.
10. The scroll plate of claim 9, wherein
said wall thickness is substantially equal to said hole
diameter.
11. The scroll plate of claim 7, wherein
said end plate has third and fourth pressure equalizing passages
formed through the plate, said third pressure equalizing passage
being formed at a distance from said center point and offset
180.degree. from said first pressure equalizing passage, said
fourth pressure equalizing passage being formed at a distance from
said center point, wherein
said third and fourth pressure equalizing passages are positioned
at locations in the end plate that prevent said third and fourth
pressure equalizing passages from simultaneously being completely
blocked by the spiral shaped wrap of the second plate at any time
when the plates rotate relative to each other.
12. The scroll plate of claim 11, wherein
a line from said center point to said third pressure equalizing
passage and a line from said center point to said fourth pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
13. A scroll-type fluid compressor, comprising
a pair of scroll plates, each having an end plate on which a spiral
shaped wrap is located; said scroll plates being arranged to
interfit said spiral shaped wraps thereby defining an interior
space comprising a series of movable, crescent shaped pockets which
reduce in volume as they move radially inwardly towards a center
point during an orbiting cycle in which one of the scroll plates
rotates relative to the other scroll plate;
at least one back-pressure pocket located adjacent to one of the
scroll plates;
first and second pressure equalizing passages formed in one of the
end plates, the pressure equalizing passages interconnecting said
interior space with said at least one back-pressure pocket, said
first pressure equalizing passage formed at a distance from a
center point of one of the scroll plates, said second pressure
equalizing passage being formed at a distance from said center
point, wherein
said first and second pressure equalizing passages are positioned
at locations in the end plate that permit said first and second
pressure equalizing passages to be in the same crescent shaped
pocket at some time, but prevent said first pressure equalizing
passage from being open in a crescent shaped pocket at the same
time said second pressure equalizing passage is open in a different
crescent shaped pocket when the plates rotate relative to each
other to thereby prevent pressure leakage between high and low
pressure crescent shaped pockets.
14. The scroll-type fluid compressor of claim 13, wherein
a line from said center point to said first pressure equalizing
passage and a line from said center point to said second pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
15. The scroll-type fluid compressor of claim 13, further
including
third and fourth pressure equalizing passages formed in the same
end plate as the first and second pressure equalizing passages,
wherein
said third and fourth pressure equalizing passages are positioned
at locations in the end plate that permit said third and fourth
pressure equalizing passages to be in the same crescent shaped
pocket at some time when the plates rotate relative to each
other.
16. The scroll-type fluid compressor of claim 15, wherein
said third pressure equalizing passage is formed at a distance from
said center point and offset 180.degree. from said first pressure
equalizing passage, said fourth pressure passage is formed at a
distance from said center point, and
a line from said center point to said third pressure equalizing
passage and a line from said center point to said fourth pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
17. The scroll-type fluid compressor of claim 13, wherein
each of said spiral shaped wraps has a wall thickness, said first
and second pressure equalizing passages are holes having a
diameter, said wall thickness being greater than or substantially
equal to said hole diameter so that the spiral shaped wrap
completely covers each hole at some time when the plates rotate
relative to each other.
18. The scroll-type fluid compressor of claim 17, wherein
said wall thickness is substantially equal to said hole
diameter.
19. The scroll-type fluid compressor of claim 13, wherein
said pressure equalizing passages are formed in an orbiting scroll
plate which is caused to orbit relative to a stationary scroll
plate.
20. The scroll-type fluid compressor of claim 13, wherein
said pressure equalizing passages are formed in a stationary scroll
plate about which an orbiting scroll plate is caused to orbit.
21. A scroll-type fluid compressor, comprising
a pair of scroll plates, each having an end plate on which a spiral
shaped wrap is located; said scroll plates being arranged to
interfit said spiral shaped wraps thereby defining an interior
space comprising a series of movable, crescent shaped pockets which
reduce in volume as they move radially inwardly towards a center
point during an orbiting cycle in which one of the scroll plates
rotates relative to the other scroll plate;
a back-pressure pocket located adjacent to one of the scroll
plates;
first and second pressure equalizing passages formed in one of the
end plates, the pressure equalizing passages interconnecting said
interior space with said back-pressure pocket, said first pressure
equalizing passage formed at a distance from said center point,
said second pressure equalizing passage being formed at a distance
from said center point, wherein
said first and second pressure equalizing passages are positioned
at locations in the end plate that prevent said first and second
pressure equalizing passages from simultaneously being completely
blocked by the spiral shaped wrap of the second plate and from
simultaneously being open in different crescent shaped pockets at
any time when the plates rotate relative to each other.
22. The scroll-type fluid compressor of claim 21, wherein
a line from said center point to said first pressure equalizing
passage and a line from said center point to said second pressure
equalizing passage define an angle equal to or greater than
90.degree. and equal to or greater than 120.degree..
23. The scroll-type fluid compressor of claim 21, further
comprising
third and fourth pressure equalizing passages formed in the same
end plate as the first and second pressure equalizing passages,
wherein
said third and fourth pressure equalizing passages are formed at
locations in the end plate that prevent said third and fourth
pressure equalizing passages from simultaneously being completely
blocked by the spiral shaped wrap of the other plate at any time
when the plates rotate relative to each other.
24. The scroll-type fluid compressor of claim 23, wherein
said third pressure equalizing passage is formed at a distance from
said center point and offset 180.degree. from said first pressure
equalizing passage, said fourth pressure passage is formed at a
distance from said center point, and
a line from said center point to said third pressure equalizing
passage and a line from said center point to said fourth pressure
equalizing passage define an angle greater than or equal to
90.degree. and less than or equal to 120.degree..
25. The scroll-type fluid compressor of claim 21, wherein
each of said spiral shaped wraps has a wall thickness, said first
and second pressure equalizing passages are holes having a
diameter, said wall thickness being greater than or substantially
equal to said hole diameter so that the spiral shaped wrap
completely covers each hole at some time when the plates rotate
relative to each other.
26. The scroll-type fluid compressor of claim 25, wherein
said wall thickness is substantially equal to said hole
diameter.
27. The scroll-type fluid compressor of claim 21, wherein
said pressure equalizing passages are formed in an orbiting scroll
plate which is caused to orbit relative to a stationary scroll
plate.
28. The scroll-type fluid compressor of claim 21, wherein
said pressure equalizing passages are formed in a stationary scroll
plate about which an orbiting scroll plate is caused to orbit.
29. A method of operating a scroll-type fluid compressor,
comprising
providing a pair of scroll plates, each having an end plate on
which a spiral shaped wrap is located in an arrangement in which
said spiral shaped wraps interfit to define an interior space
comprising a series of movable, crescent shaped pockets which
reduce in volume as they move radially inwardly towards a center
point during an orbiting cycle in which one of the scroll plates
orbits relative to the other scroll plate;
rotating said orbiting scroll plate relative to the other scroll
plate to cause said crescent shaped pockets to move radially
inwardly and increase in pressure;
providing continuous communication between said interior space and
a back pressure pocket located adjacent to one of said scroll
plates through pressure equalizing passages formed through one of
the end plates while preventing communication between crescent
shaped pockets at different pressures by preventing said first and
second pressure equalizing passages from simultaneously being open
in different crescent shaped pockets.
30. The method of operating a scroll-type fluid compressor of claim
29, including
positioning first and second pressure equalizing passages in the
same crescent shaped pocket at some time when the plates rotate
relative to each other.
31. The method of operating a scroll-type fluid compressor of claim
30, including
positioning third and fourth pressure equalizing passages in the
same crescent shaped pocket at some time when the plates rotate
relative to each other.
32. The method of operating a scroll-type fluid compressor of claim
29, including
preventing first and second pressure equalizing passages from
simultaneously being completely blocked by the spiral shaped wraps
of the plates at any time when the plates rotate relative to each
other.
33. The method of operating a scroll-type fluid compressor of claim
32, including
preventing third and fourth pressure equalizing passages from
simultaneously being completely blocked by the spiral shaped wraps
of the plates at any time when the plates rotate relative to each
other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to scroll-type compressors, and more
particularly to a pressure equalizing passage configuration that
improves the efficiency and other performance characteristics of
scroll-type compressors.
2. Description of the Related Art
A scroll-type compressor is a high efficiency compressor used in
air conditioning systems, vacuum pumps, expanders, and engines. An
example of the prior art configuration is illustrated in FIGS. 1-3.
Scroll compressor 10 comprises a hermetic casing 20, a shaft 30, a
fixed scroll plate 40, orbiting scroll plate 50, and upper frame.
Each scroll plate 40 and 50 has a spiral shaped wrap 41 and 51,
respectively. These wraps interfit to form an interior space and a
series of crescent shaped pockets (illustrated in FIG. 3). A
pressure equalizing passage 52 is formed in the orbiting scroll
plate to interconnect the interior space with back-pressure pocket
80 of air bushing 90.
The orbiting scroll wrap 51 is rotationally displaced 180.degree.
relative to the stationary scroll wrap 41. An orbiting movement is
imparted to the orbiting scroll 50 by an Oldham's coupling 70
fitted into a lower frame 60. The Oldham's coupling 70 translates
rotational movement, e.g., from a rotating shaft 30, to an orbiting
movement. A typical orbiting scroll will orbit at about 3600 rpm.
As the orbiting scroll 50 orbits around the stationary plate 40,
line contacts created between the interfitted wraps form crescent
shaped pockets which begin to move radially inwards towards the
center of the plates. As the crescent shaped pockets move radially
inwards they reduce in volume, and therefore compress the fluid
contained within the pockets. A discharge port at the center of one
of the plates receives high pressure from the crescent shaped
pockets when they terminate at the center. By this process, low
pressure fluid is introduced at the exterior perimeter of the
plates and is encased within the crescent shaped pockets as the
pockets begin to form. As the pockets move inwardly, the fluid
pressure increases until the fluid is discharged through the
discharge port.
The scroll-type compressor has many advantages over other
compressors, such as reciprocating compressors. First, the
continuous movement of the scroll-type compressor does not require
recompression or re-expansion. Second, the continuous and smooth
operation of the scroll-type compressor eliminates problems
associated with the reciprocating movement of other compressors
(e.g., metal fatigue is reduced), and produces about one tenth of
the torque. Third, the crescent shaped pockets are paired and
offset at 180.degree. thereby reducing non-symmetrical pressures
and the vibrations and noise attendant thereto. Finally, because of
their efficiency, scroll-type compressors may be smaller and
lighter, and require fewer parts, resulting in lower manufacturing
costs.
One of the most important concerns in scroll-type compressor
efficiency is the tendency of the crescent shaped pockets to leak.
Leakage can occur either though the vertical line contacts formed
at the orbiting and stationary scroll plate interface at the front
or back end of each pocket, or at the horizontal seals formed at
the tips of a wrap 41a and 51a and the flat surface of the opposing
scroll plate 51b and 41b. Most fluid pressure loss is through the
horizontal seals.
Therefore efforts have focused on minimizing fluid leakage past the
tips of the wraps. One way of doing so is to minimize the clearance
between scroll tips and the opposing plates. However, increasing
the contact pressure on the scroll plate tips will cause premature
wearing of the wrap tips and decrease the service life of the
scroll plate.
The opposite problem is created by the pressure increase within the
interior space which tends to produce an axial force separating the
scroll plates. To counteract this separating axial force, air
bushings 90 have been used. These air bushings 90 have
back-pressure pockets 80 which are interconnected with the interior
space through pressure equalizing passages 52. Therefore, as the
pressure in the interior space increases, the counteracting
pressure in the back-pressure pocket will increase accordingly,
thereby improving the efficiency of the compressor. An example of a
prior art scroll-type compressor having this configuration is
described in U.S. Pat. No. 4,557,675 to Murayama et al.
Applicants have studied this prior art configuration and discovered
that certain problems are encountered during operation. FIG. 3
demonstrates the operation of a scroll-type compressor.
As shown in FIG. 3A, an arbitrarily selected point in the
compression cycle, the pressure equalizing passage 52 will not be
covered by the stationary scroll wrap 41. During an orbiting motion
cycle, however, the tip of the stationary scroll wrap 41 begins to
cover up the pressure equalizing passage 52. As the cycle
progresses, the pressure equalizing passage 52 becomes completely
covered (See FIG. 3C) and "exits" from the stationary scroll wrap
on the other side to another, lower pressure crescent shaped pocket
(See FIGS. 3D and 3E). When the wrap covers the pressure equalizing
passage, it interferes with the communication between the interior
space and the air bushing's back-pressure pocket. This interference
has a deleterious effect on the overall performance of the
scroll-type compressor. During the interference, the pressure in
the crescent shaped pocket increases while the pressure in the
back-pressure pocket remains constant. The resulting pressure
imbalance axially forces the scroll plates apart and causes leakage
past the wrap tips. Although this interference occurs during a very
brief time period, it nonetheless represents a significant portion
of the cycle.
For example, FIG. 6 illustrates the cyclical path of a pressure
equalizing passage formed in the orbiting scroll. As the passage
passes underneath the wrap tip 41 the intercommunication between
the interior space and the air bushing's back-pressure pocket is
interrupted. This interruption occurs over 60.degree.-70.degree. of
the 360.degree. cycle. In other words blockage of the pressure
equalizing passage occurs during 60/360-70/360 or 16.7%-19.4% of
the orbiting cycle; the compressor fails to operate at peak
efficiency during almost 20% of the compression cycle. The same
problem occurs when two pressure equalizing passages are
symmetrically formed in the scroll plate; because they are
symmetrically configured, they are blocked at the same stage of
each cycle.
SUMMARY OF THE INVENTION
The advantages and purpose of the invention will be set forth in
part in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The advantages and purpose of the invention will be
realized and attained by means of the elements and combinations
particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purpose of the
invention, as embodied and broadly described herein, the invention
comprises a scroll plate for use in a scroll-type fluid compressor,
having an end plate with a center point, and a spiral shaped wrap
for interfitting with a spiral shaped wrap on a second scroll plate
to thereby form a series of moveable, crescent-shaped pockets which
reduce in volume as they move radially inward towards the center
point. The end plate has a first hole formed therein at a distance
from the center point and a second hole formed therein at a
distance from the center point, wherein the first and second holes
are formed in the end plate such that the first and second holes
will be in the same crescent shaped pocket during at least a
portion of a crescent shaped pocket's radially inward movement. The
first and second pressure equalizing passages are positioned at
locations in the end plate that prevent the first and second
pressure equalizing passages from simultaneously being completely
blocked by the spiral shaped wrap of the second plate at any time
when the plates rotate relative to each other.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory, and are not restrictive of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a sectional view of a scroll-type fluid compressor.
FIG. 2 is a sectional view of a portion of a scroll-type fluid
compressor showing two interfitting scroll plates.
FIGS. 3A-3E are views showing a prior art scroll plate during a
compression cycle.
FIGS. 4A-4E are views showing a scroll plate according to the
invention during a compression cycle.
FIGS. 5A-5E are views of another scroll plate configuration during
a compression cycle.
FIG. 6 is a view showing the relative movement between a pressure
equalizing passage and a stationary scroll plate wrap.
FIG. 7 is a diagram showing the relative pressures in a crescent
shaped pocket and a back-pressure pocket in a prior art device.
FIG. 8 is a diagram showing the relative pressures in a crescent
shaped pocket and a back-pressure pocket in a device according to
the invention.
FIGS. 9A-9F are views showing a scroll plate configuration
according to a second embodiment of the invention during a
compression cycle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 4A-4E demonstrate the compression cycle of a scroll wrap
having a pressure equalizing passage configuration according to the
invention. In FIG. 4A a stationary scroll wrap 41 intermeshes with
an orbiting scroll wrap 51. The orbiting scroll plate has two holes
53 and 54 drilled through its end plate. The holes are configured
so that there is never a time in the cycle of the scroll plate
orbit that communication between the interior space and the back
pressure passage is interrupted.
FIG. 4A illustrates the interaction between the orbiting scroll
wrap 51 and stationary scroll wrap 41 at an arbitrarily selected
portion of the compression cycle. The orbiting scroll wrap 51 is
formed on the orbiting scroll plate 50, and the stationary scroll
wrap 41 is formed on the stationary scroll plate 40. In FIG. 4A,
both pressure equalizing passages 53 and 54 are in the same
crescent shaped pocket. As the cycle progresses (FIG. 4B) one of
the pressure equalizing passages 53 is beginning to be covered by
the stationary scroll wrap 41. The other pressure equalizing
passage 54 is left open to continue to interconnect the back
pressure pocket with the crescent shaped pocket 100. The cycle
progresses and the pressure equalizing passage 53 that is covered
by the stationary scroll wrap 41 continues to pass underneath the
stationary scroll wrap 41 (see FIGS. 4C and D) to the other side
where it "exits" from underneath the stationary scroll wrap 41 into
another crescent shaped pocket, while at the same time, the other
pressure equalizing passage 54 is now covered by the pressure
equalizing wrap 41 (See FIG. 4E).
According to this configuration, the first pressure equalizing
passage is positioned at the "optimal point," a position on the
orbiting scroll wrap that has been determined to be a position in
which there will be good axial compliance, i.e., the pressure in
the back pressure passage 80 is adequate to keep the axial seal
between the tips 41a and 51a, and the plate surfaces 41b and 51b on
the scroll plates. The second pressure equalizing passage 54 is
positioned at a higher pressure position (i.e., at a point
"downstream" in the wrap spiral. This ensures that the minimum
pressure in the back pressure pocket will be adequate to maintain a
good seal between the wrap tips and the opposing scroll plates,
while if the pressure increases, it will increase in accordance
with the increased pressure in the crescent shaped pockets. At no
point, however, are both of the pressure equalizing passages
blocked and, therefore, the pressure in the interior space does not
overwhelm the effective functioning of the back pressure pocket as
it does in the prior art configuration. (Compare FIG. 7 with FIG.
8).
FIGS. 5A-5E illustrate what may happen if the pressure equalizing
passages are spaced too far apart. FIG. 5A illustrates the
interaction between the orbiting scroll wrap 51 and stationary
scroll wrap 41 at an arbitrarily selected portion of the
compression cycle. The orbiting scroll wrap 51 is formed on the
orbiting scroll plate 50, and the stationary scroll wrap 41 is
formed on the stationary scroll plate 40. In FIG. 5A both pressure
equalizing passages 53 and 54 are in the same crescent shaped
pocket. As the cycle progresses (FIG. 5B) one of the pressure
equalizing passages 53 is beginning to be covered by the stationary
scroll wrap 41, leaving the other pressure equalizing passage 54
open to continue to interconnect the back pressure pocket with the
crescent shaped pocket 100. The cycle progresses and the pressure
equalizing passage 53 that is covered by the stationary scroll wrap
41 continues to pass underneath the stationary scroll wrap 41 (see
FIGS. 5C and 5D) to the other side where it "exits" from underneath
the stationary scroll wrap 41 into another, lower pressure crescent
shaped pocket. In this non-preferred configuration, however, the
other pressure equalizing passage 54 is not now covered by the
pressure equalizing wrap 41, but, rather stays open in the higher
pressure crescent shaped pocket (See FIG. 5E). A pressure leak will
therefore develop from the higher pressure crescent shaped pocket
to the lower pressure crescent shaped pocket with a corresponding
loss in volumetric efficiency.
The inventors have therefore determined the pressure equalizing
passages should be spaced at a distance between 90 and 120 degrees
from each other. The inventors have also determined that the
pressure equalizing passages should be substantially equal in width
to the wrap wall thickness (See FIG. 9F). In other words, if the
size of the pressure equalizing passage is equal to the wrap wall
thickness or as close to the wrap thickness as possible and still
be entirely blocked by the wrap, the blockage time is minimized and
the compressor will be more efficient. If the size of the pressure
equalizing passage is too large in comparison with the wrap
thickness, a pressure leak from high to low pressure crescent
shaped pockets will occur.
FIGS. 9A-9E illustrate a second embodiment of the invention. FIG.
9A illustrates the interaction between the orbiting scroll wrap 51
and stationary scroll wrap 41 at an arbitrarily selected portion of
the compression cycle. The orbiting scroll wrap 51 is formed on the
orbiting scroll plate 50, and the stationary scroll wrap 41 is
formed on the stationary scroll plate 40. In FIG. 9A both pressure
equalizing passages 53 and 54 are in the same crescent shaped
pocket. A second set of pressure equalizing passages 33a and 34a
are also formed offset from the first set of pressure equalizing
passages 53 and 54 by 180 degrees. Because of this 180 degree
offset, pressure equalizing passage 33a correlates with pressure
equalizing passage 53 and pressure equalizing passage 34a
correlates with 54.
As the cycle progresses (FIG. 4B) the first correlating pressure
equalizing passages 53 and 33a are beginning to be covered by the
stationary scroll wrap 41, leaving the other pressure equalizing
passages 54 and 34a open to continue to interconnect the back
pressure pocket with the crescent shaped pocket 100. Because the
pressure equalizing passages 54 and 34a are offset by 180 degrees,
there is no pressure leakage between their respective crescent
shaped pockets--their internal pressures will be approximately
equal at all relevant times. The cycle progresses and the pressure
equalizing passages 53 and 33a which are covered by the stationary
scroll wrap 41 continue to pass underneath the stationary scroll
wrap 41 (see FIGS. 9C and 9D) to the other side where they "exit"
from underneath the stationary scroll wrap 41 into other crescent
shaped pockets, while at the same time, the other pressure
equalizing passages 54 and 34a are now covered by the pressure
equalizing wrap 41 (See FIG. 4E). Thus, at least two pressure
equalizing passages are located in crescent shaped pockets having
approximately equal pressures at all times. The resulting
improvement in volumetric efficiency increases the overall
efficiency of the compression cycle.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the disclosed process
and product without departing from the scope or spirit of the
invention. For instance, the pressure equalizing passages may be
formed in the stationary scroll in the event the back pressure
pocket is positioned to provide the axial sealing force to the
stationary scroll. Other embodiments of the invention will be
apparent to those skilled in the art from consideration of the
specification and practice of the invention disclosed herein. It is
intended that the specification and examples be considered as
exemplary only.
* * * * *